Embodiments of the present inventive concept relate to a complementary metal oxide semiconductor image sensor (CIS), and more particularly to: an image sensor which may perform a fast operation by using one of differential ramping up/down signals, applying a correlated double sampling to a pixel signal, and reducing an entire analog-to-digital conversion time; an operation method thereof; and devices having the image sensor.
As an analog-to-digital conversion method of an image sensor, a single-slope analog digital converting method is widely used. The method compares a ramping signal with a pixel signal having a constant voltage level, and converts timing or time when a voltage level of the ramping signal equals to a voltage level of the pixel signal according to a result of the comparison into a digital signal.
In a column parallel analog-to-digital conversion method, one column analog-to-digital converter needs to be integrated in one pixel pitch, so that the single slope analog-to-digital conversion method is widely used in consideration of layout area and power consumption. Recently, as the number of pixels of an image sensor has dramatically increased, a demand for a fast operation of the image sensor has also increased.